Conventionally, as one of the parts which are in charge of communication functions, a bar antenna using a bar core whose material is a ferrite of a ferromagnetic material is widely used. However, the ferrite is formed by ceramics such as iron oxide mainly, and so there exists a drawback that the ferrite has a low impact resistance and is very brittle. In particular, if the bar core is formed to an elongated form having thin thickness, the bar core is broken easily sometimes. With regard to the bar antenna having the broken bar core, the inductance of the bar antenna decreases and the resonance frequency thereof changes, and so communication at a desired frequency cannot be made.
Therefore, means that the bar antenna itself has a flexible structure is proposed. For example, in Japanese Laid-open Patent Application Publication No. H08-271659, as illustrated in FIG. 8, a structure of a bar antenna for a radio wave clock is disclosed. In a bar antenna of a radio wave clock, as a structure of the bar antenna whose performance is not deteriorated by a damage due to impact or pressure and whose improvement in quality becomes possible, the following structure of the bar antenna is disclosed. The bar antenna 1 includes a plurality of bar cores 2, a bobbin 6 of a hollow shape made of a synthetic resin, and a winding 3 being wound on the outer periphery of the bobbin 6. A space is provided between each of the bar cores 2, a bent portion 6a is provided in a portion matching with the space, and the bar cores 2 are connected in a line and held in the inside of the bobbin 6. Such a structure can prevent the damage of the bar core due to impact or pressure by falling of the radio wave clock, and in an assembling process of the antenna during manufacturing, can aim to improve the reliability of the radio wave clock, and thereby reduce the cost by the structure for improving impact resistance of the antenna and by the quality assurance (refer to Abstract and FIG. 1 of Japanese Laid-open Patent Application Publication No. H08-271659). Here, the sign given to each element in this paragraph and FIG. 8 is the sign described in Japanese Laid-open Patent Application Publication No. H08-271659, and is of this paragraph only.
Further, from the standpoint of the reliability of the communication function of the bar antenna, means for protecting the bar core from external forces by the pressure or the impact has been proposed. For example, Japanese Laid-open Patent Application Publication No. 2001-358522 discloses a structure of a bar antenna, as illustrated in FIG. 9, including, as means for preventing damage to a single bar core and for increasing the reliability of the bar core, a single bar core 3 made of a thin rod-like ferromagnetic body, a bobbin 4 holding a winding being wound to the bar core 3 in an insulating state and wrapping the bar core 3, a case 5 accommodating the bar core 3 and the bobbin 4, and a potting material 6 sealing the bar core 3 and the bobbin 4 in the case 5. Such a structure can isolate the bar core 3 from the degradation factors as temperature and humidity, vibration, and the like by the potting material 6 (refer to Abstract and FIG. 1 of Japanese Laid-open Patent Application Publication No. 2001-358522). Here, the sign given to each element in this paragraph and FIG. 9 is the sign described in Japanese Laid-open Patent Application Publication No. 2001-358522, and is of this paragraph only.
However, since in the invention of Japanese Laid-open Patent Application Publication No. H08-271659, the winding is wound across a plurality of bar cores being divided, there exists a problem that the possibility of being unable to communicate at a predetermined frequency depending on the degree of deformation in the winding portion across the bar cores, that is, the bending portion cannot be excluded. Further, since in the invention of Japanese Laid-open Patent Application Publication No. H08-271659, the bobbin wrapping the single bar core is sealed in the case using the potting material, there exists a problem that the possibility that the bar core breaks in the vicinity of the center of the winding when a strong external force or an impact is applied cannot be excluded. Meanwhile, a case of adapting a remote or automatic operation in place of the manual operation by human operation of various devices that are around us is increasing. For example, in an automobile, in order to perform unlocking of the door by receiving a radio wave from a remote control device that a driver has, or to perform unlocking of the door automatically when a portable device that a driver carries approaches a certain distance, some means carries out polling for communicating even when the car is parking and consumes battery power. Further, when it is intended to extend the distance in which the communication is possible, it is brought to increase the current supplied to the antenna, and so a situation occurs that the power consumption increases and the load to the battery increases.
In order to prevent such a situation, it is desirable to use a high output antenna having a high output per one piece without increasing the power consumption. In that case, it is preferable to increase the length of the bar core. However, in the prior art described above, there is a problem that it is difficult to constitute the length of the bar core to be long, while the bar antenna has a high impact resistance and can exert the function thereof continuously even if being bent. It is because, since in the invention of Japanese Laid-open Patent Application Publication No. H08-271659, the winding is wound across a plurality of bar cores being divided, even if the length of the divided bar core is taken longer further, the possibility of being unable to communicate at a predetermined frequency depending on the degree of the deformation of the bending portion still cannot be excluded, and in the invention of Japanese Laid-open Patent Application Publication No. 2001-358522, by increasing the length of the single bar core, the impact resistance decreases and when the bar core breaks, the predictability of the break portion, furthermore, the frequency change is lowered further.